A composite proton exchange membrane and its preparation method

Abstract

This invention belongs to the field of polymer materials technology, and particularly relates to a composite proton exchange membrane and its preparation method. The composite proton exchange membrane prepared by this invention uses perfluorosulfonic acid resin (PFSA) suitable for industrial application as the base membrane material. By adding modified polybenzimidazole polymer resin, the problem of high ion permeation rate in existing PFSA proton exchange membranes is solved, reducing interpenetration of the electrolyte during use, significantly reducing cross-contamination between the positive and negative electrode electrolytes, and extending the electrolyte's lifespan. This invention functionalizes poly(bifluorosulfonic acid) resin (PBI), enhancing its proton transport capacity. The proton exchange membrane formed by blending functionalized PBI with PFSA resin maintains excellent vanadium blocking ability while also possessing excellent proton transport capacity and high ion selectivity. The preparation process of this invention is simple, and the resulting proton exchange membrane meets the performance and long-term stability requirements of flow batteries.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a composite proton exchange membrane and its preparation method. Background Technology

[0002] To achieve safe, clean, and large-scale renewable energy storage systems, flow batteries (RFBs) have garnered significant attention in the fields of electrical and chemical energy due to their superior battery efficiency, rapid response, long cycle life, and unique modular design, enabling the storage and release of electrical energy. The proton exchange membrane (PEM), a key component of the vanadium redox flow battery (VRFB) system, serves to isolate the positive and negative electrode electrolytes and provides the necessary proton transport channels. An excellent PEM should possess characteristics such as high proton conductivity, low vanadium ion permeability, excellent physicochemical stability, and low cost. Therefore, researching PEMs with superior comprehensive performance has become a hot topic in the current flow battery field.

[0003] Perfluorosulfonic acid resin is currently the only proton exchange membrane material that can be industrially applied. Its unique molecular structure gives it excellent mechanical and chemical stability, while its highly hygroscopic side chains provide excellent proton conductivity. DuPont's Nafion series membranes are currently the most widely used proton exchange membranes for flow batteries, exhibiting excellent proton conductivity. However, their excessively rapid ion permeation rate leads to cross-contamination of the positive and negative electrolytes, reducing battery efficiency and membrane lifespan, increasing battery operating costs, and severely limiting the effective use of sulfonic acid resin proton exchange membranes in flow batteries.

[0004] Chinese patent document CN117457953A discloses a perfluorosulfonic acid resin slurry and a proton exchange membrane for flow batteries, as well as a method for preparing the same. The method for preparing the perfluorosulfonic acid resin slurry includes the following steps: (1) dissolving and dispersing perfluorosulfonic acid resin in a mixed solvent to obtain a semi-finished perfluorosulfonic acid resin slurry; (2) adding the semi-finished perfluorosulfonic acid resin slurry to a high-pressure homogenizer for high-pressure homogenization to obtain the final perfluorosulfonic acid resin slurry. By subjecting the semi-finished perfluorosulfonic acid resin slurry to high-pressure homogenization, the perfluorosulfonic acid resin molecular chain segments in the obtained perfluorosulfonic acid resin slurry are uniformly distributed and oriented, resulting in high uniformity, low viscosity, and good fluidity of the perfluorosulfonic acid resin slurry. However, the high-pressure homogenizer is used to disperse the semi-finished perfluorosulfonic acid resin slurry. The high shear force brought by the high-pressure homogenizer will cause the molecular chains of the polymer resin to break, resulting in mechanical / shear degradation, reducing the molecular chain and affecting the film-forming performance of the product. Secondly, the high-pressure homogenizer will bring significant thermal effects. The high pressure and shear force are converted into heat, causing the solvent in the material to volatilize, affecting the solution system, and thus affecting the metal ion permeability performance of the proton exchange membrane.

[0005] The method of preparing composite proton exchange membranes by adding inorganic materials is an effective way to improve the ability of proton exchange membranes to block metal ion penetration. However, the dispersibility and solubility of inorganic materials limit the application of this method.

[0006] Therefore, providing a proton exchange membrane for flow batteries with low metal ion permeability and its preparation method has positive practical significance for improving electrolyte lifespan and battery cycle stability. Summary of the Invention

[0007] To address the problem of high metal ion permeability in perfluorosulfonic acid resin proton exchange membranes, this invention provides a composite proton exchange membrane and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A composite proton exchange membrane is composed of perfluorosulfonic acid resin and functionalized polybenzimidazole, wherein the content of functionalized polybenzimidazole is 0.1%-60% by mass.

[0010] Preferably, the thickness of the proton exchange membrane is 10~250 μm.

[0011] More preferably, the thickness of the proton exchange membrane is 40~60 μm.

[0012] Preferably, the perfluorosulfonic acid resin has an ion exchange capacity of 0.5~2.5 mmol / g and a molecular weight of 150,000~800,000; more preferably, it has an ion exchange capacity of 0.8~1.8 mmol / g and a molecular weight of 200,000~600,000; and most preferably, it has an ion exchange capacity of 0.9~1.1 mmol / g and a molecular weight of 250,000~350,000.

[0013] Preferably, the functionalized polybenzimidazole includes one or more of phosphate-doped polybenzimidazole, fluorinated polybenzimidazole, and alkylated polybenzimidazole.

[0014] Preferably, the molecular weight of the polybenzimidazole is 50,000 to 400,000; more preferably, it is 300,000 to 400,000.

[0015] A further preferred embodiment is the preparation of the phosphoric acid-doped polybenzimidazole: PBI is mixed with a high-concentration phosphoric acid aqueous solution, heated under a nitrogen atmosphere to form a homogeneous solution, dried and cooled to obtain phosphoric acid-doped PBI.

[0016] More preferably, in the preparation of the phosphoric acid-doped polybenzimidazole, the mass ratio of PBI to high-concentration phosphoric acid aqueous solution is 1:2-1:4, the mass concentration of phosphoric acid in the high-concentration phosphoric acid aqueous solution is ≥85%, and the reaction temperature is 180-200℃.

[0017] More preferably, the preparation of the fluorinated polybenzimidazole is as follows: PBI is added to pentafluorobenzoyl chloride, and the reaction is carried out at 80-180℃ for 8-48 hours under a nitrogen atmosphere. After filtration and drying, fluorinated PBI is obtained, wherein the mass ratio of PBI to pentafluorobenzoyl chloride is 1:1-1:5.

[0018] Further preferably, the preparation of the alkylated polybenzimidazole is as follows: under a nitrogen atmosphere, PBI powder is mixed with NMP and stirred at 80-180°C to dissolve. NaH is added for dispersion. After dispersion, 1-bromohexane is added, and the mixture is heated for 8-32 hours. After the reaction is completed, the mixture is cooled to room temperature, and methanol is added to precipitate the product. The precipitate is washed with methanol and deionized water and dried to obtain alkylated PBI. In this case, PBI accounts for 5-15 wt% of the mass of NMP, the mass ratio of PBI to NaH is 1:2-1:5, and the mass ratio of PBI to 1-bromohexane is 1:1-1:3.

[0019] Preferably, the composite proton exchange membrane contains 15%-50% functionalized polybenzimidazole by mass.

[0020] More preferably, the composite proton exchange membrane contains 20%-50% polybenzimidazole doped with phosphate by mass.

[0021] More preferably, the composite proton exchange membrane contains 15%-25% fluorinated polybenzimidazole by mass.

[0022] More preferably, the composite proton exchange membrane contains 15%-25% alkylated polybenzimidazole by mass.

[0023] The present invention also provides a method for preparing the above-mentioned composite proton exchange membrane, comprising the following steps:

[0024] (1) Dissolve perfluorosulfonic acid resin and functionalized polybenzimidazole in an organic solvent to obtain a film-forming dispersion;

[0025] (2) The film-forming dispersion described in step (1) is uniformly coated onto the substrate surface by solution casting to form a liquid film, and then dried by heating with a temperature gradient of 25~200℃.

[0026] Preferably, the film-forming dispersion in step (1) has a solid content of 5-60% and a viscosity of 30-2000 mPa / s; the coating speed in step (2) is 10-100 cm / min and the film thickness is 50-300 μm; and the substrate is a glass plate.

[0027] More preferably, the solid content of the film-forming dispersion in step (1) is 20-30%, and the viscosity is 100-300 mPa / s; the coating speed in step (2) is 40-60 cm / min, and the liquid film thickness is 190-210 μm.

[0028] Preferably, the organic solvent in step (1) is one or more of alcohol, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0029] Compared with the prior art, the present invention has at least the following advantages:

[0030] 1. This invention functionalizes polybenzimidazole and then mixes it with perfluorosulfonic acid resin to prepare a composite proton exchange membrane by solution casting. This solves the problem of high ion permeation rate in existing perfluorosulfonic acid proton exchange membranes, effectively reducing cross-permeation of metal ions, thereby improving the charge-discharge efficiency and long-term cycle stability of the proton exchange membrane; it also reduces electrolyte cross-contamination, thereby reducing electrolyte usage costs, making it easier to apply in the industrialization of flow battery stacks, and helping to achieve the requirements of long life and high performance of proton exchange membranes, thus reducing the usage cost of the stack.

[0031] 2. This invention enhances the proton transport capacity of PBI by functionalizing it, enabling the proton exchange membrane formed by blending functionalized PBI with perfluorosulfonic acid resin to maintain excellent vanadium blocking ability while also retaining excellent proton transport capacity and high ion selectivity. Specifically, phosphorylated and alkylated PBI not only improve the solubility and proton conductivity of pure PBI, but also retain the vanadium blocking ability of the imidazole ring backbone of PBI in the proton exchange membranes formed by blending phosphorylated and alkylated PBI with perfluorosulfonic acid resin. Furthermore, the improved hydrophobicity and vanadium blocking ability of fluorinated PBI result in a proton exchange membrane formed by blending fluorinated PBI with perfluorosulfonic acid resin exhibiting superior performance in blocking vanadium ion permeation.

[0032] 3. This invention proposes for the first time three different preparation methods for functional PBI. The preparation methods are simple and convenient, can be completed in one step, and can control the reaction time and reaction temperature, control the degree of functionalization, and achieve controllable modification of functional PBI. Attached Figure Description

[0033] Figure 1 The samples of Examples 2, 5, and 8 and Comparative Examples 1 and 2 of this invention were tested at 80-200 mA / cm². 2 Below is a comparison chart of battery performance tests. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0035] Preparation of phosphoric acid-doped PBI: PBI was mixed with a high-concentration phosphoric acid aqueous solution and heated to 180°C under nitrogen protection to form a homogeneous solution. The solution was then dried and cooled to obtain phosphoric acid-doped PBI. The mass ratio of PBI to the high-concentration phosphoric acid aqueous solution was 1:2, and the mass concentration of the high-concentration phosphoric acid aqueous solution was 85%.

[0036] Preparation of fluorinated PBI: PBI was added to pentafluorobenzoyl chloride and reacted at 150°C for 24 h under a nitrogen atmosphere. The mixture was then filtered and dried to obtain fluorinated PBI. The mass ratio of PBI to pentafluorobenzoyl chloride was 1:4.

[0037] Preparation of alkylated PBI: Under a nitrogen atmosphere, PBI powder was mixed in a certain amount of NMP (PBI accounted for 5 wt% of NMP mass), stirred and dissolved at 80℃, and a certain amount of NaH was slowly added, with a mass ratio of PBI to NaH of 1:2. After dispersion, a certain amount of 1-bromohexane was slowly added, with a mass ratio of PBI to 1-bromohexane of 1:2. The reaction was heated for 24 hours. After the reaction was completed, the mixture was cooled to room temperature, and 500 ml of methanol was added to precipitate the product. The precipitate was washed with methanol and deionized water and dried to obtain alkylated PBI.

[0038] In all the following examples and comparative examples, the molecular weight M of the perfluorosulfonic acid resin used is... n The molecular weight is 300,000, and the ion exchange capacity (IEC) is 1.0 mmol / g; the molecular weight M of polybenzimidazole is... n It is 350,000.

[0039] Example 1

[0040] 20g of perfluorosulfonic acid resin and 5g of phosphoric acid-doped polybenzimidazole were added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 110mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0041] Example 2

[0042] 20g of perfluorosulfonic acid resin and 10g of phosphoric acid-doped polybenzimidazole were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 128mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0043] Example 3

[0044] 20g of perfluorosulfonic acid resin and 20g of phosphoric acid-doped polybenzimidazole were added to 120g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 155mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0045] Example 4

[0046] 20g of perfluorosulfonic acid resin and 5g of fluorinated polybenzimidazole were added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 130mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0047] Example 5

[0048] 20g of perfluorosulfonic acid resin and 10g of fluorinated polybenzimidazole were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 162mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0049] Example 6

[0050] 20g of perfluorosulfonic acid resin and 20g of fluorinated polybenzimidazole were added to 120g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 210mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0051] Example 7

[0052] 20g of perfluorosulfonic acid resin and 5g of alkylated polybenzimidazole were added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 122mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0053] Example 8

[0054] 20g of perfluorosulfonic acid resin and 10g of alkylated polybenzimidazole were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 145mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0055] Example 9

[0056] 20g of perfluorosulfonic acid resin and 20g of alkylated polybenzimidazole were added to 120g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 190mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0057] Comparative Example 1

[0058] 20g of perfluorosulfonic acid resin and 10g of polybenzimidazole (PBI) were added to 90g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 160mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0059] Comparative Example 2

[0060] 25g of perfluorosulfonic acid resin was added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 105mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film. The coating speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating of 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0061] Comparative Example 3

[0062] 25g of polybenzimidazole was added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 250mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film. The coating speed was 50cm / min and the liquid film thickness was 200μm. After gradient heating of 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0063] Comparative Example 4

[0064] 25g of phosphoric acid-doped polybenzimidazole was added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 185mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0065] Comparative Example 5

[0066] 25g of fluorinated polybenzimidazole was added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 270mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0067] Comparative Example 6

[0068] 25g of alkylated polybenzimidazole was added to 75g of DMF solvent to form a film-forming dispersion with a solid content of 25% and a viscosity of 223mPa / s. The film-forming dispersion was uniformly coated onto the surface of a glass plate by solution casting to form a liquid film at a casting speed of 50cm / min and a liquid film thickness of 200μm. After gradient heating at 25℃ (6min) - 50℃ (6min) - 80℃ (6min) - 140℃ (6min) - 180℃ (6min), a composite proton exchange membrane with a thickness of 50μm was prepared.

[0069] Table 1 shows the proton conductivity, vanadium ion permeability, and ion selectivity data for examples and comparative examples of PBI doped with different functionalizations. Compared with pure perfluorosulfonic acid resin, the addition of functionalized PBI significantly improves the vanadium ion permeability and ion selectivity of the proton exchange membrane, resulting in superior overall performance.

[0070] The test methods for proton conductivity and vanadium ion permeability are in accordance with the industry standard NB / T 42080-2023.

[0071] Table 1. Basic physical properties of different membrane samples

[0072]

[0073] Figure 1 The samples from Examples 2, 5, 8 and Comparative Examples 1, 2 were tested at 80-200 mA / cm². 2 The following is a comparison chart of battery performance tests. At various current densities, the coulombic efficiency (CE) and energy efficiency (EE) of Examples 2, 5, and 8 are superior to those of Comparative Examples 1 and 2, indicating that the proton exchange membranes of Examples 2, 5, and 8 have better performance in all aspects. The test results basically correspond to the physicochemical properties. Example 5 has the lowest vanadium ion permeability, and therefore has the best coulombic efficiency (CE); Example 2 has the highest ion selectivity, and therefore has the best energy efficiency (EE).

[0074] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite proton exchange membrane, characterized in that, The proton exchange membrane is composed of perfluorosulfonic acid resin and functionalized polybenzimidazole. The content of functionalized polybenzimidazole is 15%-50% by mass. The functionalized polybenzimidazole includes fluorinated polybenzimidazole; a composition of phosphate-doped polybenzimidazole and fluorinated polybenzimidazole; a composition of fluorinated polybenzimidazole and alkylated polybenzimidazole; and a composition of fluorinated polybenzimidazole, phosphate-doped polybenzimidazole and alkylated polybenzimidazole. The preparation of phosphoric acid-doped polybenzimidazole is as follows: PBI is mixed with a high-concentration phosphoric acid aqueous solution, heated under a nitrogen atmosphere to form a homogeneous solution, dried and cooled to obtain phosphoric acid-doped PBI. The mass ratio of PBI to the high-concentration phosphoric acid aqueous solution is 1:2-1:4, the mass concentration of phosphoric acid in the high-concentration phosphoric acid aqueous solution is ≥85%, and the reaction temperature is 180-200℃. The preparation of the fluorinated polybenzimidazole: PBI is added to pentafluorobenzoyl chloride and reacted at 80-180℃ for 8-48h under a nitrogen atmosphere. After filtration and drying, fluorinated PBI is obtained. The mass ratio of PBI to pentafluorobenzoyl chloride is 1:1-1:

5. Preparation of the alkylated polybenzimidazole: Under a nitrogen atmosphere, PBI powder is mixed with NMP and stirred at 80-180℃ to dissolve. NaH is added for dispersion. After dispersion, 1-bromohexane is added, and the mixture is heated for 8-32 hours. After the reaction is completed, the mixture is cooled to room temperature, and methanol is added to precipitate the product. The precipitate is washed with methanol and deionized water and dried to obtain alkylated PBI. The PBI accounts for 5-15 wt% of the mass of NMP, the mass ratio of PBI to NaH is 1:2-1:5, and the mass ratio of PBI to 1-bromohexane is 1:1-1:

3.

2. The composite proton exchange membrane as described in claim 1, characterized in that, The thickness of the proton exchange membrane is 10~250 μm.

3. The composite proton exchange membrane as described in claim 1, characterized in that, The composite proton exchange membrane contains 20%-50% phosphate-doped polybenzimidazole by mass; the composite proton exchange membrane contains 15%-25% fluorinated polybenzimidazole by mass; and the composite proton exchange membrane contains 15%-25% alkylated polybenzimidazole by mass.

4. The method for preparing the composite proton exchange membrane according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Dissolve perfluorosulfonic acid resin and functionalized polybenzimidazole in an organic solvent to obtain a film-forming dispersion; (2) The film-forming dispersion described in step (1) is uniformly coated onto the substrate surface by solution casting to form a liquid film, and then dried by heating with a temperature gradient of 25~200℃.

5. The preparation method according to claim 4, characterized in that, The film-forming dispersion in step (1) has a solid content of 5-60% and a viscosity of 30-2000 mPa / s; the coating speed in step (2) is 10-100 cm / min and the film thickness is 50-300 mm.

6. The preparation method according to claim 4, characterized in that, The organic solvent in step (1) is one or more of the following: alcohol, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

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